Hithertofore, it is known that 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one derivatives have physiological activities and applications thereof as various medicinals have been studied.
For instance, the 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one derivatives represented by the general formula ##STR1## wherein R.sub.1 stands for an alkyl group or an aryl group; R.sub.2 stands for a hydrogen atom, a halogen atom, a nitro group, a carbakoxy group or an alkyl group; R.sub.3 stands for an alkyl group or an aralkyl group; Y.sub.1 stands for --SO-- or --SO.sub.2 --, is known to be effective for controlling propagation of cancer cells (Japanese Laying-Open Patent Publication No. 52-118494 (1977)).
The 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one derivatives represented by the general formula ##STR2## wherein R.sub.4 stands for a 1H-tetrazol-5-yl group, a 2H-tetrazol-5-yl group, a carboxyl group or an alkoxycarbonyl group; R.sub.5 stands for an aryl or heteroaryl group unsubstituted or substituted with an alkyl group, an alkoxy group, a hydroxy group or halogen; X.sub.1 stands for an alkylene group, an alkenylene group, or an alkynylene group, which may have an oxygen atom or a sulfur atom or --SO.sub.2 -- at its end and may be substituted with one or more straight chain alkyl groups, cyclic alkyl groups or R.sub.5, and their physiologically acceptable salts are known to have excellent anti-allergic activity (Japanese Laying-Open Patent Publication No. 58-177997 ('83)).
As described above, several kinds of 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one derivatives are known by now. However, their biological activities relate to medicines, and nothing is known about their biological activities as agricultural chemicals.
The object of the invention is to provide a novel 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one derivatives which has excellent biological activities as an agricultural chemical and a useful agricultural-horticultural fungicide preparation containing said derivative.
We paid attention to the thiadiazolopyrimidin-5-one skeleton, which is known to be useful as medicinal, and synthesized many novel derivatives thereof. As a result, we found that a specific class of 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one derivatives exhibit very excellent biological activities as agricultural fungicides. On the basis of this finding, we have completed this invention.